The present invention relates to systems and devices used to load containers and pallets. More particularly, the present invention relates to a robotic system used to load mail trays and tubs of different shapes and sizes on pallets and into wheeled containers and carts.
Millions of pieces of mail are deposited with the postal service every day. The deposited mail is sorted, generally by zip or other code, and shipped to the proper destination. Generally, the sorting process involves placing mail with the same or related codes into tubs or trays. Thus, each tub or tray will contain mail addressed to geographically proximate locals. The tubs and trays are then placed on pallets and carts and the pallets and carts are loaded on trucks or other vehicles for shipment to their appropriate destinations.
Some parts of this process have been automated, including the sorting of mail by zip code. However, the loading of tubs and trays onto pallets and carts is generally done by hand. While hand or manual loading accomplishes the desired result, it requires postal staff to be engaged in physically demanding and tedious work. Moreover, the speed at which pallets and carts can be loaded is limited by the speed at which the human body can operate and the number of people that can economically be employed to carry out the task. With ever increasing mail demands, faster, more efficient methods of loading pallets and containers with mail tubs and trays are needed.
Accordingly, the present invention provides an automated system for loading pallets and containers with mail trays and tubs. The present invention may be implemented in a system that in one embodiment includes two cells, each with a gantry robot, although the invention can be implemented with one cell. Each cell includes an open frame that is secured to a hard surface such as the concrete floor of a building. The sides of the frame may be enclosed with a mesh. A number of doors are provided in the mesh walls to provide access to the interior of the cell. The top of the cell is open and includes two tracks on which the robot travels. The robot is mounted on the cell such that it can move in a horizontal plane along two axes. A conveyor system for trays and tubs passes through the cells.
The robot includes a robot arm that is extendible in a vertical plane which is perpendicular to the plane in which the robot moves. A mechanical wrist is coupled to the end of the robot arm and an end effector or gripper is mounted on the wrist. In one embodiment, the gripper includes a plurality of fluid-actuated offset fingers that are used to lift trays and tubs firm the conveyor system and deliver them to wheeled containers, carts, and pallets. The gripper can accommodate a variety of mail trays, flats, and tubs, including United States Postal Service (xe2x80x9cUSPSxe2x80x9d) Managed Mail (xe2x80x9cMMxe2x80x9d), Extended Managed Mail (xe2x80x9cEMMxe2x80x9d), and Short Managed Mail (xe2x80x9cSMMxe2x80x9d) trays. The mail trays and tubs can be delivered by the gripper with or without outer sleeves and straps. The trays and tubs are delivered to a variety of containers and pallets including USPS Eastern Region Mail Carts (xe2x80x9cERMCsxe2x80x9d), General Purpose Mail Carts (xe2x80x9cGPMCsxe2x80x9d), USPS pallets, and other similar pallets.
The offset-finger gripper is designed to grasp the mail trays/tubs from the sides and bottom. The fingers rotate 90 degrees to release the grasped tray/tub when the clamp cylinder is relaxed. The gripper uses a multiple pressure clamp cylinder which allows the selection of high or low clamp force to accommodate and adjust to heavy tubs and lightweight trays. The gripper also includes a valve and proximity switch, which permit the clamp cylinder to be adjusted at both an intermediate open position and a full open position. This feature allows the robot to pick up a tray/tub from a direction perpendicular to the product""s long axis. It also shortens clamp travel to close, improving speed performance and system throughput.
The present invention utilizes a top-loading technique. Mail containers are approached from the top and loaded into carts and onto pallets in a similar fashion. Top loading requires less room for the gripper to actuate and, thus, reduces the floor space needed for the system. A top loading system has several other advantages, including the ability to load open-top carts without opening or removing side doors or side netting (although doors and netting on at least one side of the cart, Such as the front, should be removed). However, in a top-loading system the height of the first level or layer of product (trays/tubs) must be known so that subsequent layers or levels may be loaded on top of it. Accordingly, the gripper is designed to detect and measure the delivered tray/tub height in the cart or on the pallet with which it is placed.
The present invention includes a mail containment plate to make height measurements. The plate is a gravity plate and moves vertically along bearing rods. Height measurements are made using a proximity switch and target and vertical robot travel values. Initially, the plate is raised when a tray or tub is located in the gripper. The robot then moves to a known height drop-off destination inside a cart or at a pallet. The gripper releases the tray or tub, which will settle on or nest in the tray or tub, if any, below it. The robot executes a vertical move upward and starts a measurement process while the containment plate stays in place on top of the mail in the delivered tray or tub. A proximity sensor senses a switch target when the end of the vertical plate travel has been reached. The current vertical position of the robot""s wrist is recorded in memory. The final delivered height of the tray or tub is now known and the next layer to be delivered is adjusted by the robot program to accommodate the previous height or position of the delivered mail tray or tub. In addition to its use in taking measurements, the containment plate also helps to prevent loose mail in unsleeved trays/tubs from falling out of the trays/tubs during robotic transportation.
In addition to the features described above, the present invention includes a feature to lower shelves in mail carts. At least one existing mail cart, the GPMC, has a pivotable shelf that is movable between a horizontal and vertical position. When using a top loading technique to load these types of carts, the cart shelf must be lowered after the bottom half of the cart has been loaded with trays/tubs. In order to lower the shelf in a GPMC, the gripper utilizes a shelf-lowering assembly in the form of a slide/cylinder assembly, which extends a shelf handling bracket and spring finger, in one embodiment, and a clip in another, to unlatch and lower the GPMC shelf. Once the slide/cylinder is extended to engage the latching mechanism on the GPMC cart, the shelf lowering process begins. The robot executes programmed moves to release the cart shelf latch while the spring finger engages the shelf to start the downward lowering motion as the shelf rests on the handling bracket. If the operation is unsuccessful due to a malfunction or jamming situation, the spring finger disengages the shelf and springs back to its original position without damage to the finger. A photoelectric sensor determines that the shelf lowering operation has been successful by checking the presence of the shelf at various stages in the lowering process.
These are just some of the features and advantages of the present invention. Others will become apparent by a review of the drawings and details described below.